The typical dosing of total daily insulin for an obese pt is 0.6 units/kg/day, so for a 300 lb pt, I'd think they'd start @ about 40 lantus then about 15 or so aspart with meals. That said, that's a base estimate which is titrated up from there as needed, so wow, this person must have really out of control diabetes!
One thing I've also seen is for bigger people is a divided dose of lantus, say 1/2 at night, 1/2 with lunch or something, which the endocrinologist said was because although lantus was theoretically giving a basal dose over 24 hours, it can be metabolized differently and effectively only cover for say, 20 hrs, so dividing the dose ensures more constant coverage.
Anyhow, the highest I've seen is 80 U, and the lady could've definitely probably gone up from there b/c her sugars were still 200+. It'd be interesting to see in your case how the dose had been titrated, ie, where did they start and how did they get here? At a certain pt too, I'd start to suspect there's more going on in this case than just 'pt needs more insulin'.